They are grease crumbs that are fried in a deep fryer.
Role in episode
After the Krusty Krab starts selling Krabby Patties with Yummy Bunz, Plankton must once again find a way to outdo Mr. Krabs. He gets the idea to do away with chum and just sell pure grease, which he burns to a crisp and sells as Crispity Crunchities. This also inspires Mr. Krabs to start selling pure grease as well, which he calls "Wow! Soup."
- In "Back to the Past," Patrick mentions a similar food item called "Crunchity Munchities" when he places a quarter in the time machine, thinking it is a vending machine.